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Thu, 21 May 2026 09:06:58 -0700 (PDT) From: Justin Suess To: gnoack3000@gmail.com, mic@digikod.net Cc: linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Justin Suess Subject: [PATCH 2/6] landlock: Add LANDLOCK_SCOPE_SYSV_MSG_QUEUE Date: Thu, 21 May 2026 12:06:36 -0400 Message-ID: <20260521160640.1716746-3-utilityemal77@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260521160640.1716746-1-utilityemal77@gmail.com> References: <20260521160640.1716746-1-utilityemal77@gmail.com> Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Add a new scoped access right LANDLOCK_SCOPE_SYSV_MSG_QUEUE for controlling operations msgget, msgsnd, msgrcv, and msgctl on SysV message queues. Merely handling msgget is insufficient; SysV message queues do not use FDs or process local handles, and the msqid associated with a queue is valid within the IPC namespace. There is no requirement to perform a msgget to interact with a SysV message queue. When a process enforces this scoping, access to SysV message queues by a restricted process is only allowed if the queue was created by a process in the same or a nested Landlock domain. When a SysV message queue is allocated by a process in a Landlock domain, the security blob for the kern_ipc_perm is updated to reflect domain provenance and the blob is tagged as a message queue via the new @kind enum. The scope is enforced from the generic ipc_permission hook rather than the per-call msg_queue_* hooks. ipc_permission is the choke point for msgget on an existing queue and for msgsnd / msgrcv / msgctl(IPC_STAT, MSG_STAT, MSG_STAT_ANY). ipc_permission also fires for semaphores and shared memory, so the hook bails out when the blob's @kind is not LANDLOCK_SYSV_IPC_MSG_QUEUE. msgctl_down() (IPC_RMID and IPC_SET) does not go through ipc_permission, so msg_queue_msgctl is kept to cover those. It also guards against the IPC_INFO / MSG_INFO case where @msq is NULL and there is no specific queue to scope. Also update the scoped_test ACCESS_LAST sentinel to track the new last scope so the unknown-scope selftest does not falsely accept LANDLOCK_SCOPE_SYSV_MSG_QUEUE as unknown. Audit records are generated for this scope on denials. Signed-off-by: Justin Suess --- include/uapi/linux/landlock.h | 3 + security/landlock/audit.c | 4 + security/landlock/audit.h | 1 + security/landlock/limits.h | 2 +- security/landlock/task.c | 137 ++++++++++++++++++ .../testing/selftests/landlock/scoped_test.c | 2 +- 6 files changed, 147 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index 10a346e55e95..c879b345afa3 100644 --- a/include/uapi/linux/landlock.h +++ b/include/uapi/linux/landlock.h @@ -398,10 +398,13 @@ struct landlock_net_port_attr { * related Landlock domain (e.g., a parent domain or a non-sandboxed process). * - %LANDLOCK_SCOPE_SIGNAL: Restrict a sandboxed process from sending a signal * to another process outside the domain. + * - %LANDLOCK_SCOPE_SYSV_MSG_QUEUE: Restrict a sandboxed process from interacting + * with a sysv msg queue created by a process outside the domain. */ /* clang-format off */ #define LANDLOCK_SCOPE_ABSTRACT_UNIX_SOCKET (1ULL << 0) #define LANDLOCK_SCOPE_SIGNAL (1ULL << 1) +#define LANDLOCK_SCOPE_SYSV_MSG_QUEUE (1ULL << 2) /* clang-format on*/ #endif /* _UAPI_LINUX_LANDLOCK_H */ diff --git a/security/landlock/audit.c b/security/landlock/audit.c index 8d0edf94037d..174ddf6bd42c 100644 --- a/security/landlock/audit.c +++ b/security/landlock/audit.c @@ -79,6 +79,10 @@ get_blocker(const enum landlock_request_type type, case LANDLOCK_REQUEST_SCOPE_SIGNAL: WARN_ON_ONCE(access_bit != -1); return "scope.signal"; + + case LANDLOCK_REQUEST_SCOPE_MSG_QUEUE: + WARN_ON_ONCE(access_bit != -1); + return "scope.sysv_msg_queue"; } WARN_ON_ONCE(1); diff --git a/security/landlock/audit.h b/security/landlock/audit.h index 56778331b58c..cc5700adab5a 100644 --- a/security/landlock/audit.h +++ b/security/landlock/audit.h @@ -21,6 +21,7 @@ enum landlock_request_type { LANDLOCK_REQUEST_NET_ACCESS, LANDLOCK_REQUEST_SCOPE_ABSTRACT_UNIX_SOCKET, LANDLOCK_REQUEST_SCOPE_SIGNAL, + LANDLOCK_REQUEST_SCOPE_MSG_QUEUE, }; /* diff --git a/security/landlock/limits.h b/security/landlock/limits.h index b454ad73b15e..7b74bcd66470 100644 --- a/security/landlock/limits.h +++ b/security/landlock/limits.h @@ -27,7 +27,7 @@ #define LANDLOCK_MASK_ACCESS_NET ((LANDLOCK_LAST_ACCESS_NET << 1) - 1) #define LANDLOCK_NUM_ACCESS_NET __const_hweight64(LANDLOCK_MASK_ACCESS_NET) -#define LANDLOCK_LAST_SCOPE LANDLOCK_SCOPE_SIGNAL +#define LANDLOCK_LAST_SCOPE LANDLOCK_SCOPE_SYSV_MSG_QUEUE #define LANDLOCK_MASK_SCOPE ((LANDLOCK_LAST_SCOPE << 1) - 1) #define LANDLOCK_NUM_SCOPE __const_hweight64(LANDLOCK_MASK_SCOPE) diff --git a/security/landlock/task.c b/security/landlock/task.c index 6d46042132ce..68ac46baa2a5 100644 --- a/security/landlock/task.c +++ b/security/landlock/task.c @@ -434,6 +434,138 @@ static int hook_file_send_sigiotask(struct task_struct *tsk, return -EPERM; } +static const struct access_masks sysv_msg_queue_scope = { + .scope = LANDLOCK_SCOPE_SYSV_MSG_QUEUE, +}; + +/** + * hook_msg_queue_alloc_security - Record the creator's domain on a SysV msg + * queue + * + * @perm: IPC permission structure of the newly created message queue. + * + * Save a reference to the creating task's Landlock domain in the IPC security + * blob and tag the blob as belonging to a message queue so that the generic + * ipc_permission hook can distinguish msg queues from sem and shm objects. + * + * Return: 0 (allocation of the blob itself is handled by the LSM core). + */ +static int hook_msg_queue_alloc_security(struct kern_ipc_perm *const perm) +{ + struct landlock_kern_ipc_perm_security *const ipc_sec = + landlock_kern_ipc_perm(perm); + const struct landlock_cred_security *const subject = + landlock_get_applicable_subject(current_cred(), + sysv_msg_queue_scope, NULL); + + ipc_sec->kind = LANDLOCK_SYSV_IPC_MSG_QUEUE; + + /* + * The blob is zero-allocated by the LSM core, so owner_subject.domain + * is already NULL for an unsandboxed creator. + */ + if (!subject) + return 0; + + landlock_get_ruleset(subject->domain); + ipc_sec->owner_subject = *subject; + return 0; +} + +/** + * hook_msg_queue_free_security - Release the creator's domain reference + * + * @perm: IPC permission structure of the message queue being destroyed. + * + * The IPC security blob itself is freed by the LSM core. + */ +static void hook_msg_queue_free_security(struct kern_ipc_perm *const perm) +{ + struct landlock_kern_ipc_perm_security *const ipc_sec = + landlock_kern_ipc_perm(perm); + + /* May be called from an RCU callback (msg_rcu_free()). */ + landlock_put_ruleset_deferred(ipc_sec->owner_subject.domain); +} + +/** + * hook_ipc_permission - Enforce SysV msg queue scoping on the current task + * + * @ipcp: IPC permission structure of the object being accessed. + * @flag: Requested mode bits (unused; same value for every msg queue access). + * + * The ipc_permission hook is the choke point for msgget on an existing queue + * and for msgsnd / msgrcv / msgctl(IPC_STAT, MSG_STAT, MSG_STAT_ANY) before + * they touch any per-message state. Using the per-message msg_queue_msgrcv hook + * instead would not work: find_msg() silently skips messages for which the + * hook returns an error and turns the result into -EAGAIN / -ENOMSG. + * + * The hook fires for sem and shm objects as well; @kind is used to filter + * them out. + * + * Return: 0 if access is allowed, -EPERM if scoped out. + */ +static int hook_ipc_permission(struct kern_ipc_perm *const ipcp, + const short flag) +{ + const struct landlock_kern_ipc_perm_security *const ipc_sec = + landlock_kern_ipc_perm(ipcp); + size_t handle_layer; + const struct landlock_cred_security *subject; + + /* Don't worry about other IPC objects for now */ + if (ipc_sec->kind != LANDLOCK_SYSV_IPC_MSG_QUEUE) + return 0; + + subject = landlock_get_applicable_subject(current_cred(), + sysv_msg_queue_scope, + &handle_layer); + if (!subject) + return 0; + + if (!domain_is_scoped(subject->domain, ipc_sec->owner_subject.domain, + sysv_msg_queue_scope.scope)) + return 0; + + landlock_log_denial(subject, &(struct landlock_request) { + .type = LANDLOCK_REQUEST_SCOPE_MSG_QUEUE, + .audit = { + .type = LSM_AUDIT_DATA_IPC, + .u.ipc_id = ipcp->key, + }, + .layer_plus_one = handle_layer + 1, + }); + /* + * What error return here technically doesn't matter; it all gets + * mapped into EACCES when it's non-zero. Return EACCES anyway for + * consistency. + */ + return -EACCES; +} + +/** + * hook_msg_queue_msgctl - Enforce scoping on msgctl(IPC_RMID, IPC_SET) + * + * @msq: IPC permission structure of the message queue, or NULL for + * namespace-wide commands (IPC_INFO, MSG_INFO). + * @cmd: msgctl command code (unused). + * + * msgctl_down() does not go through ipc_permission(), so this hook is + * needed to cover IPC_RMID and IPC_SET. IPC_INFO and MSG_INFO are + * namespace-wide queries with no specific queue, so they are not in scope + * for SysV msg queue scoping. + * + * Return: 0 if access is allowed, -EPERM if scoped out. + */ +static int hook_msg_queue_msgctl(struct kern_ipc_perm *const msq, const int cmd) +{ + /* IPC_INFO and MSG_INFO are queue-less; nothing to scope. */ + if (!msq) + return 0; + + return hook_ipc_permission(msq, 0); +} + static struct security_hook_list landlock_hooks[] __ro_after_init = { LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check), LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme), @@ -443,6 +575,11 @@ static struct security_hook_list landlock_hooks[] __ro_after_init = { LSM_HOOK_INIT(task_kill, hook_task_kill), LSM_HOOK_INIT(file_send_sigiotask, hook_file_send_sigiotask), + + LSM_HOOK_INIT(msg_queue_alloc_security, hook_msg_queue_alloc_security), + LSM_HOOK_INIT(msg_queue_free_security, hook_msg_queue_free_security), + LSM_HOOK_INIT(msg_queue_msgctl, hook_msg_queue_msgctl), + LSM_HOOK_INIT(ipc_permission, hook_ipc_permission), }; __init void landlock_add_task_hooks(void) diff --git a/tools/testing/selftests/landlock/scoped_test.c b/tools/testing/selftests/landlock/scoped_test.c index b90f76ed0d9c..6692ba0573e6 100644 --- a/tools/testing/selftests/landlock/scoped_test.c +++ b/tools/testing/selftests/landlock/scoped_test.c @@ -12,7 +12,7 @@ #include "common.h" -#define ACCESS_LAST LANDLOCK_SCOPE_SIGNAL +#define ACCESS_LAST LANDLOCK_SCOPE_SYSV_MSG_QUEUE TEST(ruleset_with_unknown_scope) { -- 2.53.0